WebService failed to load file or assembly "ESRI. Arcgis.xxx "or one of its dependencies

Development environment: Windows7 flagship 64bit, VisualStudio2008 with SP1, ArcEngine10.0, NetFrameWork4.0, IIS7, and C # development language.

Write Arcengine write the WebService analysis function, and an error occurs while the compilation is running.

Error message: Failed to load file or assembly "ESRI. Arcgis.xxx, version=10.0.0.0, XXX "or one of its dependencies. The system cannot find the file specified.

Viewed on the internet for a long time, that is to change the build platform to X86, but I do not have this option here, and can not create this option, so this is not applicable (before the CS project encountered a similar problem is modified in this way).

It was later discovered to be an issue with the IIS application pool, as long as the Enable 32-bit application option for the application pool used by the program is set to true.